Two identical carts on a horizontal, nearly frictionless track collide and stick together. Cart P moves to the right at 2m/s just before impact, while cart Q is at rest. Which of the following best describes the kinetic energy of the two-cart system immediately after the collision compared with the kinetic energy immediately before the collision?
a) It is the same because kinetic energy is conserved in any collision on a frictionless surface.
b) It is one-half as large because some kinetic energy is transformed into other forms during the collision.
c) It is greater by a factor of two because the total mass doubles while the speed remains the same.
d) It is one-fourth as large because the speed of the carts is halved during the collision.